1. Field of the Invention
The invention relates to a method for noise suppression in images of an image sequence.
2. Description of the Background Art
It is known in the field of digital image processing that characteristic picture disturbances occur in accordance with the properties of the sensors used for image acquisition. Digital images recorded under unfavorable lighting conditions or having a high proportion of dark image areas exhibit a relatively high noise level. Filtering methods which improve the signal-to-noise ratio are generally used in order to reduce the dominating photon noise present in the images. As a rule, for this purpose a time filter is applied to the regions of the images in which no movement is present. A detection of moved image contents is carried out on the basis of the change in intensity determined for each separately considered pixel. It is assumed that a pixel is in movement when the fluctuation in intensity between images of a sequence overshoots a threshold value which is directly related to the standard deviation of the noise. These pixels determined as being in motion are not filtered, or are filtered only slightly. Processing with a rigid recursive time filter as described in patent U.S. Pat. No. 6,314,160 B1, is applied to the pixels determined as static or immobile. The use of a recursive low-pass as a filter base limits the maximum averaging length over an image sequence. The method therefore has a limited quality of noise suppression and a slow transient response.